Brain-function measurement devices using the principles of near-infrared spectroscopy (Near-infrared spectroscopy: NIRS) (see PTL 1, NPL 1) can be used as medical and research equipment or for checking educational effects and rehabilitation effects, health management at home, and market research such as commercial-product monitoring. Also, the devices can be used for tissue oxygen-saturation-degree measurement or oxygen metabolism measurement of muscle tissues by similar methods. Furthermore, the devices can be also used for general absorption spectroscopy apparatuses including sugar-content measurement of fruits.
Therefore, recently, demands for small light measurement devices such as during-exercise blood-flow monitors, saliva measurement, intraoperative brain oxygen monitors, etc. including brain-function measurement based on NIRS are increasing more and more. The specifications (wavelengths, the number of measurement points, sampling speed, etc.) of the small devices like these have to change measurement parts and the number of measurement channels (the number of measurement points) by depending on applications, and, conventionally, dedicated specifications had to be prepared for each of the applications. Therefore, it has been difficult to realize a module-type biophotonic measurement device for a common base, and it has been difficult to reduce the cost of the device supporting application of small NIRS, which are increasing more and more.
In such circumstances, PTL 2 discloses a method in which measurement regions and the number of channels can be freely set, detachable transmission/reception units are provided, and a main control unit adjusts timing by controlling a sub control unit of the attached transmission/reception unit to obtain measurement data about brain activities. Moreover, PTL 3 discloses a method in which, in order to realize a module-type photodetector which is detachable/attachable and excellent in safety, light receiver and light transmitter are made into modules, and, particularly in the light receiver, a high-voltage power source for driving a photodetector is housed in a package which can be fixed to the head.